1. Field of the Invention
The present invention relates to a method of and an apparatus for detecting an end point of etching, and more particularly to a method of and an apparatus for detecting by emission spectroscopy an end point of etching of a specimen, such as the substrate of a semiconductor device, to be etched by plasma treatment.
2. Description of the Invention
As an apparatus for detecting by emission spectroscopy an end point of etching of a specimen such as the substrate of a semiconductor device to be etched by plasma treatment, there is known, for example, one which is disclosed in Japanese Patent Laid-Open No. 303086/1988. According to this conventional art, an electric output signal from a photoelectric converter is stored as a standard signal in a storage of normal emission in a storage when the cloudiness of a window member is within a permissible range. A member of monitoring the state of the cloudiness compares an actual signal from the photoelectric converter with the standard signal and generates an output corresponding to the result of such comparison. Based on this output signal, a signal for the required correction will be transmitted to the member of detecting an end point of etching. Thus, even when the level of the output signal from the photoelectric converter to the member of detecting an end point of etching is lowered because of the cloudiness of the window member, the end point of the etching treatment can be detected while correction is being made for the member to detect an end point of etching. Thus, the detection of an end point thereof is carried out accurately.
In this conventional art, however, nothing has been disclosed as to how the actual signal of the photoelectric converter can be compared with the standard signal to obtain a signal to instruct correction. How the signal to instruct correction is added to the member of detecting an end point of etching has not been disclosed, either. Also, this conventional art describes that even when the level of the signal output of the photoelectric converter to the member to detect an end point of etching is lowered because of the cloudiness of the window member, the end point of etching treatment can be detected while correction is being made for the member to detect an end point of etching. However, if the end point of etching treatment must be detected while correction is being made for the member to detect the end point thereof, there may be a fear that an accurate detection of the end point of etching becomes impossible depending on some case where a treatment time for etching is, for example, very short requiring the immediate detection of an end point of etching. In such case, the end point thereof has come while correction is still being made. In other words, the end point thereof may have been detected before a final correction was still to be made. Also, since the end point of etching is detected while correction is being made, there arises the problem of a delay in the treatment time.
In addition to this conventional art, there are known ones using emission spectroscopy for detecting an end point of etching which are disclosed in Japanese Patent Laid-Open No. 65424/1987 and Japanese Patent Laid-Open No. 165920/1987.
The conventional art disclosed in Japanese Patent Laid-Open No. 65424/1987 describes that while etching a specimen, the first waveform of emission intensity and a waveform n thereof are compared with each other without any correction at each time, and with the differential value thus obtained, those of n+1 are corrected, making it easier to carry out the detection of an end point of etching. However, according to this conventional art, there arises a problem of affecting accuracy adversely because the correction should be made in the next treatment in accordance with the previous data.
Another conventional art disclosed in Japanese Patent Laid-Open No. 165920/1987 describes that a signal at the time of previous treatment is compared with an input signal, and if there is any differential value between them, the value of the electric signal will be adjusted to be identical to the signal at the time of previous treatment, by changing a gain value of the photoelectric converter so that any detection of an end point of etching in the same process can be conducted by the same detecting value even when the quantity of emission collected by the photoelectric converter is changing because of the cloudiness of the observation window or the like. However, this conventional art will result in a delay in the time between the output signal transmitted by the comparing function and the response thereto by an adjustment function.
Furthermore, there are known ones concerning the apparatus of this kind, which are disclosed in Japanese Patent Laid-Open No. 60772/1985, Japanese Patent Laid-Open No. 93940/1987, Japanese Patent Laid-Open No. 128124/1987, U.S. Pat. No. 4,615,761, Ser. No. 07/000,368 and others.